outer part of the venous plexus the large radial vein takes origin, whilst from its inner part springs the posterior ulnar vein. Both of these vessels have already been traced along the forearm to their terminations. While still upon the dorsum of the hand each communicates with the deep veins in the palm of the hand. Cutaneous Nerves.-Several cutaneous nerves have already been traced to the integument of the forearm, viz., the anterior and posterior branches of the internal cutaneous nerve to the inner aspect, and the cutaneous part of the musculo-cutaneous and lower external cutaneous branch of the musculo-spiral upon the outer aspect of the limb. Some additional twigs make their appearance by piercing the fascia in the lower third of the forearm (Figs. 17 and 18). The Palmar Cutaneous Branches are small twigs which supply the skin of the palm. The twig from the ulnar nerve takes origin about the middle of the forearm, but it does not at once pierce; the deep fascia. It proceeds downwards on the ulnar artery, and becomes superficial immediately above the annular ligament, and close to the outer side of the insertion of the flexor carpi ulnaris tendon into the pisiform bone. It is here, therefore, that it must be sought for (Fig. 17, p. 62). The palmar cutaneous branch of the median nerve appears through the deep fascia in the interval between the tendons of the flexor carpi radialis and the palmaris longus muscles, immediately above the wrist. It is continued downwards. into the palm (Fig. 17, p. 62). The palmar branch of the radial nerve runs close to the outer border of the lower part of the forearm. It does not spring from the trunk of the radial nerve, but from that branch of it which goes to the outer margin of the thumb. It is joined by a twig from the musculo-cutaneous nerve, and proceeds downwards in front of the tendon of the extensor ossis metacarpi pollicis, to end in the skin covering the ball of the thumb (Fig. 17, p. 62). Dissection. In tracing the nerves which appear on the back of the limb, it will be necessary to remove the skin from the dorsal aspect of the thumb and fingers. The great flap of skin which is still attached at the roots of the fingers may be detached, and an incision can then be made along the middle of the dorsal aspect of each digit. The skin should be carefully raised from each finger in two flaps and thrown outwards and inwards. Dorsal Cutaneous Branches.-The dorsal branch of the ulnar nerve winds round the inner margin of the wrist to reach the dorsum of the hand. It will be found immediately below the prominence formed by the lower end of the ulna, and it at once divides into three main terminal branches. Of these, the innermost runs along the ulnar margin of the dorsum of the hand, and is continued onwards along the inner margin of the little finger. The second branch proceeds towards the cleft between the little finger and the ring finger, and divides into two twigs which supply the contiguous sides of these digits. The third branch joins a twig from the radial, and the nerve thus formed runs towards the interval between the ring finger and the middle finger, and divides to supply their adjacent margins. Each of these three main branches give several minute filaments to the integument on the dorsum of the hand (Fig. 18, p. 64). The radial nerve will be found winding round the outer margin of the forearm, about two inches above the extremity of the styloid process of the radius. It at once gives off a long twig which proceeds along the radial margin of the hand and thumb. A little further on the radial nerve breaks up into four terminal branches, which are distributed as follows: the first supplies the ulnar side of the thumb; the second goes to the radial side of the index finger; the third divides to supply the adjacent sides of the index and middle fingers; whilst the fourth joins with a twig from the dorsal branch of the ulnar (as already described) to supply the contiguous margins of the middle and ring fingers. It should be noted that, except in the cases of the thumb and little fingers, the dorsal collateral nerves do not reach the extremities of the digits. The skin on the back of the lower parts of the digits is supplied by twigs, which proceed backwards from the palmar collateral nerves. As already stated, it is from the branch of the radial, which goes to the outer side of the thumb, that the radial palmar cutaneous nerve arises. Numerous fine filaments are given to the skin on the dorsum of the hand, and a certain amount of crossing of the adjacent ulnar and radial twigs takes place in this locality; in other words, twigs from the one nerve invade the territory which is occupied by the other nerve. The Deep Fascia, which envelops the forearm, should now be cleaned by removing the subcutaneous adipose tissue. It is an aponeurosis of great strength and density. More particularly is this the case on the posterior aspect of the limb, and also in the lower third of the forearm, where the fleshy bellies of the subjacent muscles give place to the tendons. In its upper part it receives an accession of fibres from the tendon of the biceps in the form of the bicipital or semilunar fascia. Some fibres are also given to it by the tendon of the triceps. Near the elbow it serves as a surface of origin for the numerous muscles which spring from the condyles of the humerus, and from its deep aspect dense septa pass between the fleshy bellies. These partitions are indicated on the surface by a series of white lines. At the wrist it becomes continuous in front with the anterior annular ligament, whilst behind it forms an obliquely placed, thickened band, the posterior annular ligament. On the dorsum of the hand the deep fascia is very thin. FRONT AND INNER BORDER OF THE FOREARM. In this dissection the following structures will be brought under the notice of the student : : 1. The radial and ulnar arteries and their banches. Dissection. With the exception of the palmar cutaneous nerves, the superficial veins and nerves on the front of the foramen may now be turned aside. The deep fascia should also be removed, and on dissecting it inwards round the ulnar border of the forearm it will be found to be firmly attached to the posterior border of the ulna. Near the elbow, as already stated, it gives origin by its deep surface to the group of muscles which spring from the internal condyle of the humerus. Where this is the case, it should be left in situ. Attempts to dissect it off will only result in laceration of the surface of the subjacent fleshy bellies, The radial artery should be followed out before the muscles are much disturbed, and at the same time the various muscles which lie upon the anterior surface of the radius, and upon which the vessel rests, should be cleaned. The Radial Artery (arteria radialis) is the smaller of the two terminal branches of the brachial artery, but the direction which it takes gives it the appearance of being the continuation of the parent trunk into the forearm. It takes origin in the anticubital fossa opposite the neck of the radius, and it proceeds downwards along the outer side of the front of the limb until it reaches the lower end of the bone. Here it turns round the outer aspect of the wrist and leaves the present dissection. At first it lies between the pronator radii teres and the supinator longus, and is overlapped to some extent on the outer side by the fleshy belly of the latter muscle (Fig. 25). Lower down it is placed between the supinator longus on the outside. and the flexor carpi radialis upon the inner side, and this position it maintains as far as the wrist. Where these muscles are fleshy the artery lies at some depth from the surface; but when the tendons make their appearance it assumes a superficial position, and is merely covered by the integument and fascia. Throughout its whole length it is closely accompanied by the venæ comites, and the radial nerve lies along its outer side in the middle third of the forearm. Above this, the nerve is separated from the vessel by a slight interval, whilst below, the nerve leaves the artery by turning round the outer margin of the forearm under cover of the supinator longus. Posteriorly the radial artery is supported by the muscles which clothe and find attachment to the front of the radius. At its origin it rests upon the tendon of the biceps; next it lies in front of the supinator brevis, with some adipose tissue intervening; from this downwards it is in contact with the pronator radii teres, the thin radial head of the flexor sublimis, the flexor longus pollicis, the pronator quadratus, and lastly, the lower end of the radius. The radial artery is usually selected for the determination of the pulse. By placing the tips of the fingers upon the lower part of the forearm, in the interval between the tendons of the supinator longus and flexor carpi radialis, the pulsations of the vessel in the living person can readily be felt. Branches of the Radial Artery. In the forearm the radial artery gives off the following branches, viz. :— 1. The radial recurrent. 2. The superficialis volæ. 3. The anterior radial carpal. 4. Muscular. : The muscular branches (rami musculares) are very numerous, and proceed from the radial artery at irregular points throughout its whole course in the forearm. The radial recurrent artery (arteria recurrens radialis) is a branch of some size. It takes origin close to the commencement of the radial artery, and in the first instance runs outwards between the supinator longus and the supinator brevis. Here it comes into relation with branches coming from the musculo-spiral nerve, and gives off several twigs for the supply of the muscles arising from the external condyle of the humerus. Somewhat reduced |